Stuck fermentation

Thu Feb 06, 2014 5:45 pm

I have read through a lot of forum discussions on stuck fermentations, but I'm looking for advice beyond the typical solutions. I've tried all that.

I brewed an all-grain 3 gallon batch of chocolate mint stout (OG 1.068), and pitched 24 grams of us-05 (very fresh). After a really quick start and active two days, fermentation stalled out at 1.030/28 (it is supposed to get down to 1.016). I am fairly certain this is not the result of under-aeration (I use a 40 gallon aquarium pump with two air stones for 30-40 minutes) or under-pitching (even at a conservative density estimate of 10 billion cells/gram 24 g for 3 gallons is plenty). I fermented at 68 F, and there were no wild swings in temperatures. I warmed it up a bit when fermentation started to slow, and when it got stuck, I stirred up the yeast cake and raised the temp to about 72. But it seems to have stalled.

I suspect I either did not rehydrate the yeast for long enough (less than 30 minutes) or (though less likely) rehydrated at too high temps. I was considering a few options:

1) I was planning on brewing a 1.060 IPA with WLP007. I could try to rack the stalled stout on top of the yeast cake from that. (If I do, is 1.060-1.065 too high an OG?)

2) Alternatively, I could make a 500 ml (or 1L?) starter of some other high attenuating yeast and pitch that into the stout. If so, do you have any recommendations as to a good yeast that would do a good job? What about one of those super high gravity yeasts that is a high attenuator and pretty alcohol tolerant?

3) Use champaign yeast. But I've heard this can generate unwanted off flavours.

I am hoping to have this brew ready for some friends who are coming to town, so I am very keen to get this to drop at least 5-7 points.
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Re: Stuck fermentation

Thu Feb 06, 2014 6:58 pm

Did you taste it?
Mash temperature was?
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Re: Stuck fermentation

Thu Feb 06, 2014 7:35 pm

Mash temp was 155F. Beersmith estimates FG of 1.016, and I trust its calculation. It's a bit cloying at 1.030.
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Re: Stuck fermentation

Thu Feb 06, 2014 10:45 pm

Another possibility is that maybe you didn't let the rehydrated slurry cool down enough, such that the yeast were shocked when added to the wort.
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